The present invention relates to lightweight metal matrix macrocomposites (MMMC) manufactured by low-melted liquid alloy infiltrating a sintered metal powdered preform with ceramic inserts distributed within. More particularly, the invention is directed to MMMC having controlled bulletproof structure and methods of the manufacture the same.
Composite materials providing protection against the impact of bullets or small-size projectiles such a grenade splinters have become standard materials for military, police, and other fields requiring security in the line of duty. Most conventional bulletproof composites are made as clothing (vests) manufactured from carbonized polymeric and ceramic fibers, for example, in the U.S. Pat. Nos. 5,448,938; 5,370,035 and 6,034,004. Though such materials are well known in the industry, they are not enough protection in many situations, e.g., against short distance impact.
There are also bulletproof structures such as doorframes as described in the U.S. Pat. No. 4,598,647 using solid materials having adequate strength to prevent penetration of a bullet, but such materials and structures are usually too complex and too heavy to be suitable in airplanes and vehicles. Solutions to this problem are very expensive and do not offer the required reliability.
Therefore, it would be desirable to use high strength lightweight metal composite materials for advantageous substitution of conventional bulletproof structures in specific applications such as airplane door frames and seat shields, or shields for the occupants of a helicopter, as well as personal protection systems.
Metal matrix composites manufactured by methods of powder metallurgy, especially by infiltrating with a molten metal, are attractive materials for structural applications not only due to their excellent properties such as stiffness, light weight, high abrasion and oxidation resistance, but mainly due to the opportunity to compose materials containing combinations of metals and ceramics that can be difficult or cost prohibitive when produced by methods of conventional metallurgy and machining.
All known infiltrated metal matrix composites can be classified in one of two big groups: (1) microcomposites containing infiltrated solid phases in the form of fine powders or fibers, and (2) macrocomposites containing whiskers, bars, or spheres having at least one dimension that is significantly larger than a cross-section of the infiltrated metal layer between such solid components.
The infiltrated microcomposites are usually brittle and exhibit insufficient flexure or fatigue strength, and low fracture toughness, which is why these materials are not used as bullet- or projectile-protective armor.
Theoretically, metal matrix macrocomposites (MMMC) can be used for these purposes, but a review of conventional MMMC showed that they all are not suitable as effective bulletproof materials because they are designed and manufactured to resist only tensile or compressive loads.
For example, a MMMC described in the U.S. Pat. Nos. 5,333,712 and 5,856,025 consist of ceramic platelets, spheres, pellets, filaments, and whiskers infiltrated with molten aluminum or Al-Mg alloy. The ceramic inserts in such composites are randomly situated in the light metal matrix, therefore, the material has irregular structure, unable to resist impact from a frontal direction. Another disadvantage of these composite structures is the lack of strength of aluminum or Al-Mg interlayers between ceramic inserts. A significant difference in mechanical properties between hard ceramic fillers and soft metal interlayers results in a low impact strength and easy crack propagation of the composite upon the whole.
Many structural modifications and methods have been proposed during the last three decades in order to increase the strength of macrocomposites: from forming barrier oxide or nitride layers (as in U.S. Pat. No. 5,501,263), to reinforcing soft interlayers with ceramic fibers (as in JP 10237566, 1998) or titanium diboride particles (as in U.S. Pat. No. 4,834,938). But, an incompatibility of soft metal matrix with hard fillers and the structural irregularity are still remained as the main drawbacks of such macrocomposites. Not one of these structures can be deemed as an efficient energy absorbing system, because crack propagation in any direction is statistically unpredictable.
The use of sacrificial composite bed is disclosed in WO 9932418, 1999 to decrease thermal stress and to eliminate cracking on the edge of the macrocomposite plate. This solution improves the dynamic strength, but also significantly increases the weight of the composite manufactured by infiltrating alumina granules with Al-5% Mg alloy melt.
Finally, aluminum and magnesium as soft infiltrating metal were substituted by titanium, zirconium, or hafnium as disclosed in the U.S. Pat. No. 5,614,308. In this case, light weight and low production cost were sacrificed in order to gain strength, and such macrocomposites could not be considered as promising materials.
All other lightweight MMMC and methods of making them known in the prior art have the same drawbacks: (a) irregular structures with statistically-undefined positions of hard inserts and soft interlayers, (b) low reproduction of mechanical properties, (c) insufficient ability to absorb impact energy and to stop crack propagation after bullet penetration through the surface layer of the protective materials, and (d) high production cost or excessive weight if the strength is provided.
The object of the invention is to design and manufacture the lightweight macrocomposite structure, able to absorb the impact energy, and to stop crack propagation after bullet or. splinter penetration through the surface of the material.
A hard, energy-absorbing, lightweight, metal matrix compatible to hard ceramic inserts must be manufactured using low-melted aluminum-magnesium alloys.
Another objective of the present invention is to design and manufacture the lightweight macrocomposite having controlled regular structure, which provides high reproduction of mechanical properties.
It is yet a further objective to provide a cost-effective manufacture of bulletproof lightweight macrocomposites.
The nature, utility, and further features of this invention will be more apparent from the following detailed description with respect to preferred embodiments of the invented technology.
The invention relates to lightweight MMMC manufactured by infiltrating solid metal powder and ceramic inserts with low-melted liquid metal or alloy. While the use of ceramic inserts and Al-Mg infiltrates has previously been contemplated in the MMMC production as mentioned above, problems related to insufficient impact strength, material reliability, compatibility of metal matrix and ceramic inserts, elimination of crack propagation, and cost cutting have not been solved.
The invention overcomes these problems by:
(1) The manufacture of MMMC containing a permeable skeleton structure of titanium, titanium aluminides (Ti3Al, TiAl, and TiAl3), or other Ti-based alloys infiltrated with aluminum, magnesium, or their alloys and 1-90 vol. % of ceramic or metal inserts positioned within said skeleton, whereby a normal projection area of each of said inserts is equal to or larger than the cross-section of a bullet or a projectile body;
(2) Manufacture, including the steps of (a) forming the permeable metal powder and inserts into the skeleton-structured preform by positioning inserts in the powder followed by loose sintering to provide the average porosity of 20-70%, (b) heating and infiltrating the resulting preform at 450-750xc2x0 C., (c) hot isostatic pressing of the infiltrated composite to heal porosity and transform it into the textured microstructure strengthened by intermetallic phases, and (d) re-sintering or diffusion annealing of the MMMC;
(3) Positioning inserts in metal powder in a predetermined geometrical pattern, filling the gaps between inserts with a metal powder, placing a new layer of inserts onto the first layer so that the second layer of inserts is placed over the spaces between the first layer inserts. This procedure may be repeated until the desired number of layers is structured.
In another aspect of the invention, a technology is provided to manufacture lightweight, bulletproof MMMC having regular energy-absorbing structure and statistically reproductive mechanical properties.
In essence, the core of the invention is to control the macrostructure of the MMMC using (a) a regular, customized pattern of positioning ceramic inserts, thus eliminating the penetration of a bullet within the entire frontal area of the composite, (b) formation of a hard metal matrix compatible with ceramic inserts and difficult for crack propagation, (c) loose sintering powders of such strong alloys as Ti-6Al-4V or TiAl together with ceramic inserts followed by the infiltration of such skeleton by Al-Mg melt, (d) dispersion strengthening of the metal matrix by sub-micron ceramic and intermetallic particles, and (e) transformation of the infiltrated metal matrix into the textured microstructure by hot isostatic pressing followed by re-sintering.
The invented technology allows the control of the macrostructure and mechanical properties of the composite materials by changing matrix composition, shape and position of inserts, number of layers, parameters of deformation, infiltration, and heat treatment, etc. The technology is suitable for the manufacture of flat or shaped metal matrix macrocomposites having improved ductility and impact energy absorption such as lightweight bulletproof plates and sheets for airplane, helicopter, and automotive applications.